Method of making texturized heat shrinkable tubing

ABSTRACT

A heat shrinkable tubing is described which has a texturized surface. Upon applying the heat shrinkable tubing to a complex shaped object and applying heat the tubing shrinks radially and linearly, uniformly so as to preserve the texturized friction surface, shrinking over depressions and expansions of the complex surface without wrinkling.

This a division of co-pending application Ser. No. 465,719 filed on Feb.11, 1983, now U.S. Pat. No. 4,576,207 issued Mar. 18, 1986.

TECHNICAL FIELD

The field of art to which this invention pertains is heat shrinkablepolymer tubing and methods of making the same.

BACKGROUND ART

Heat shrinkable tubing has been in existence for many years. The use ofheat shrinkable tubing, when properly formulated, provides a quick andeconomical method of covering various materials for a variety ofpurposes. For example, heat shrinkable tubing may be applied to amaterial for electrical insulation purposes, for protection against theelements, or to improve the feel of the material to the hand. Because ofthe wide variety of uses of such material there is an ongoing search forways to improve the tubing itself, the manner in which it can beapplied, improvement in its appearance, and its performance in the heatshrink operation. For example, it has been known that when applying heatshrinkable tubing to complex shaped articles containing many bends,expanded and depressed areas, that the tubing can have a tendency towrinkle upon shrinkage, particularly at the inside radius of curvedportions of the article to be covered. Accordingly, any improvements inheat shrinkable tubing have the potential of opening up entire new areasof use for such articles.

DISCLOSURE OF THE INVENTION

The present invention is directed to heat shrinkable tubing extrudedwith raised portions on its surface so as to provide improved propertiesand performance of such tubing in use. Such improved performance cantake the shape of improved grippability, esthetic appearance, heatdissipation, electrical insulating properties etc. The tubing is alsoformed so as to have a substantially lengthwise shrinkage so when placedover a material to be covered it conforms to bends, depressed andexpanded areas with no wrinkling. The raised portions on the tubing arealso extruded onto the heat shrinkable tubing so as to providemaintenance of a textured pattern even after heat shrinking.

Another aspect of the invention includes a method of making such tubingby melting polymer in an extruder barrel, extruding the polymer througha forming die so as to produce a textured pattern, and cooling theextruded material, the extrusion and cooling performed under tensionhere (as well as elsewhere in the manufacturing process) so as toprovide a negative elastic memory, thus insuring the above-describedsmooth conformity to complex shaped substrates.

The foregoing, and other features and advantages of the presentinvention, will become more apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a typical heat shrinkable tubing according to the presentinvention.

FIG. 2 shows a typical heat shrinkable tubing according to the presentinvention after heat treatment on a complex shaped article.

FIG. 3 shows typical apparatus useful for forming tubing according tothe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Polyvinyl chloride is a typical polymeric material useful for making thetubing according to the present invention. However, because of its costand polymeric properties such as abrasion resistance, other materialsuch as silicone, polyolefin, neoprene, ethylene-propylene-dieneterpolymer, resins, etc. can also be utilized (either alone or inadmixture) based on the correlation of polymer properties and intendeduse. These materials are purchased commercially in either pellet orgranular form and fed as such into extrusion apparatus.

The polymeric material is extruded in

continuous lengths and typically wrapped upon a take-up reel afterformulation. The inner diameters and thicknesses of the tubing varydepending on the intended use of the product but will typically rangefrom about 40 mils to about 5 inches in expanded inside diameter withrecovered wall thicknesses ranging from 5.0 mils to 0.3 inch.

While the preferred texturized patterns on the heat shrinkable tubingare raised, substantially parallel lines (a "corduroy" pattern) anypattern which provides raised or uneven portions on the surface of theotherwise smooth tubing are acceptable. For example, intermittent ratherthan continuous lines may be used.

As formed, the heat-shrink material according to the present inventiontypically contains about 5% to about 30% longitudinal shrinkage memory.Such memory is built into the tubing by processing under tension asdescribed below. This allows the tubing to be heat-shrunk over a varietyof complex shapes without creasing, crimping or wrinkling upon shrinkageonto the intended substrate. Furthermore, the texturized surface shrinksuniformly not only providing a comfortable friction-grippable surfacebut a pleasant decorative finish as well. Because its surface has beenincreased by the texture, the ability of this tubing to dissipate heatduring use is substantially increased.

In FIG. 1 the heat shrinkable tubing 1 is shown with raised ribs 2. Acomparison with FIG. 2 showing the same tubing with the same ribs afterheat shrinkage over a metal bar, demonstrating the uniformity of thetubing of the present invention.

Referring to FIG. 3 a better understanding of the method isdemonstrated. Polymeric pellets or granules 31 are added to the extruderhopper 32. The polymeric material is reduced to a plastic state in theheated barrel 33 of the extruder and is forced by a rotating screw inthe barrel 33 through extrusion head 34. The extruded tubing immediatelyis drawn through cooling bath 35 while it is held in tension. Followingexit from the cooling bath the tubing is wrapped up on take-up reel 36.Following extrusion and takeup, the tubing is unwound and reheated, forexample, by passing it through heating fluid (such as Carbowax). Apositive pressure (e.g. air) is imparted to the inside of the heatedtubing to cause the desired degree of radial expansion. At the sametime, the desired degree of linear shrinkage characteristics areimparted to the reheated tubing by holding it in tension, for examplebetween a pinch roller and capstan device.

Shrinkage of the extruded tubing is effected by any heat sourceconventionally used in this art such as a hot air blower, infraredheater, oven, heat tunnel, etc. Since a 5% to 30% longitudinal shrinkagememory is built into the tubing, a corresponding linear excess ofmaterial should be used to ensure proper coverage of any article beingcovered.

As stated, FIG. 2 shows a typical application for the heat shrinkabletubing according to the present invention for a complex shaped handlegrip with extensive bends 22, bulges 23, and depressions 24 covered withthe heat shrinkable tubing according to the present invention and heatedwith a forced hot air dryer. As can be seen from the figure a smoothwrapped handle grip results with evenness of the textured patternproviding a uniform, decorative and comfortable grip. As can beappreciated such product is particularly useful for: tennis racquethandles, bats, hammers, ax handles, shovels, roller covers for poweredconveyors, corrosion protection with increased heat transfer efficiencyfor heat transfer tubes, combined heat dissipation and electricalprotection for sensitive electrical and electronic parts, anti-rattlecoverings for automotive harnesses, comfort grip handle covers forlawnmowers, snowblowers, bicycle handle bars, etc. It should be notedthat by virtue of its greatly increased surface area as compared toconventional smooth heat shrinkable tubings, heat transfer by thisimproved product is greatly enhanced.

While this invention has been described for a tubing which incorporatesan appreciable degree of longitudinal shrinkage which provides forsmooth crimp-fee application to curved and bent substrates, a texturedproduct to be applied to straight substrates, where lengthwise shrinkageis not needed can also be made without significant lengthwise shrinkage.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

We claim:
 1. A method of making heat shrinkable tubing comprisingmelting polymeric material, extruding such material through a die toproduce a pattern of substanially parallel raised portions extendingexternally across its entire length, while in a heated state imposingpositive pressure to the interior of the tubing to impart radialshrinkage memory to the tubing and holding such tubing under lineartension to provide about 5% to about 30% longitudinal shrinkage memoryto the tubing, cooling the tubing and rolling the tubing on a take-upreel resulting in tubing capable of shrinking in response to heat overbent, expanded and depressed substrate material in uniform, unwrinkledfashion.
 2. A method of forming a texurized surface on a complex shapedobject comprising placing a heat shrinkable tubing having a texturizedsurface of substanially parallel raised portions extending along itsentire length, and about 5% to about 30% longitudinal shrinkage memoryon the complex shaped object, applying heat to the tubing causing thetubing to shrink both radially and lineraly thus forming unwrinkled,decorative, uniform texturized surface on the complex shaped object.